1. Field of the Invention
The present invention relates to motorcycle tires for uneven terrain.
2. Description of the Related Art
FIG. 4 shows a conventional motorcycle tire 2. The tire 2 is used for running on uneven terrain such as mountain forests and wilderness. The tire 2 is for uneven terrain. The tire 2 includes a tread 4, sidewalls 6, beads 8, a carcass 10, and a belt 12.
The carcass 10 includes a first ply 14a and a second ply 14b. The first ply 14a and the second ply 14b each extend on and between the beads 8 located on both sides, and each extend under and along the tread 4 and the sidewalls 6. The first ply 14a and the second ply 14b are each turned up around each bead 8 from the inner side to the outer side in the axial direction.
The first ply 14a and the second ply 14b are each formed of multiple cords aligned with each other, and a topping rubber, which are not shown. An absolute value of an angle of each cord relative to the equator plane usually ranges from 65 degrees to 90 degrees. The carcass 10 has a radial structure.
The belt 12 is located outwardly of the carcass 10 in the radial direction. The belt 12 is layered over the carcass 10. The belt 12 reinforces the carcass 10. In the tire 2, a stiffness is high in a region of the tread 4. In the tire 2, a stiffness is low in regions of the sidewalls 6.
The tire 2 has a problem that load is concentrated on the regions of the sidewalls 6 having a low stiffness, and heat is likely to be generated in the regions of the sidewalls 6. In order to enhance the stiffness of the regions of the sidewalls 6, a turned-up structure of each ply 14 of the carcass 10 has been sometimes studied. An exemplary study thereof is disclosed in JP2007-131139 (US2007/0102089).
In uneven terrain, a road surface is uneven. A vehicle running on the uneven terrain repeats jumping and landing. To the tire 2 mounted to this vehicle, not only a great mechanical load is vertically applied, but also the load is frequently applied. Therefore, when a vehicle is running on the uneven terrain, heat is likely to be generated in the regions of the sidewalls 6 of the tire 2, as compared to when the vehicle is running on a general public road. The tire 2 has a problem that fatigue of the regions of the sidewalls 6 and deterioration in performance are accelerated.
In order to restrain increase of temperature in the regions of the sidewalls 6, a fin may be provided on the outer surface of the sidewall 6. However, the tire 2 cannot exert sufficient cooling effect.
In order to enhance a stiffness of the regions of the sidewalls 6, the first ply 14a and the second ply 14b may be each turned up such that ends 16a and 16b of the first ply 14a and the second ply 14b are located close to ends 18a and 18b of the belt 12. In this case, stiffness is excessively increased, to deteriorate handling stability.
An object of the present invention is to make available a motorcycle tire for uneven terrain which has its durability improved without deteriorating handling stability.